1. Field of the Invention
The invention relates to a method of removing hydrocarbons from a solid particulate material, preferably from contaminated sludge containing hydrocarbons and solid particles. Even more preferably, the invention is directed to a method of removing oil from contaminated sludge from oil refineries, ballast sludge in supertankers, and also a method of removing hydrocarbons from drill cuttings contaminated with oil-based drilling fluids.
2. Description Of Related Art
Contaminated sludge from oil refineries, drilling operations, and other chemical and industrial operations often contain solid particles of different physical and chemical compositions, hydrocarbons, and water. One object of the present invention is to efficiently remove and recover hydrocarbons from the contaminated sludge. A preferred embodiment of this invention involves treating a specific type of contaminated sludge, namely, "drill cuttings," which are collected at drilling sites. During drilling operations, the drilling fluid or "mud" is circulated down into the wellbore to lubricate the drill bit and also to remove rock particles from the formation being drilled. A problem exists regarding the disposal of these drill cuttings, particularly when the drilling fluid or mud is oil-based or hydrocarbon-based. That is, the oil from the drilling fluid (as well as any oil from the formation) becomes associated or adsorbed to the surfaces of the drilling cuttings. The drill cuttings are then an environmentally hazardous material, and disposal is often a problem. The present invention offers an advantageous method of treating the drill cuttings, preferably at the location of the drilling rig, e.g., as a separate step for the drilling cuttings.
Solid-liquid separation processes in general have been used to remove solids from liquid phases with varying degrees of success. Currently, industry uses expensive filtration and centrifuge operations as well as heat and chemical treatments to treat contaminated sludge and other waste materials. A major problem industry is facing, however, is the separation and recovery of hydrocarbons from contaminated sludge. One reason for these difficulties is the fact that hydrocarbons bind to the surface of solid particles in the contaminated sludge, and to some extent, the hydrocarbons are absorbed by the solid particles, making recovery of the hydrocarbons more difficult. Furthermore, it is difficult to remove and recover hydrocarbons from concrete particulate solid surfaces because the hydrocarbons occupy the crevices between the particles.
It is known that various chemical treatments are useful to remove hydrocarbons from solid particles. These attempts have certain shortcomings. Most notably, some of these chemical treatments contain harsh solvents, including hydrocarbon based solvents, and other toxic elements, all of which can be harmful to the environment. Also, some of these chemical treatments react with the hydrocarbon, thereby preventing recovery of the hydrocarbon. Furthermore, since some of the chemical treatments react with the hydrocarbon, the chemical treatment can often not be reused or recycled. Still further, some chemical treatments are ineffective in removing and recovering certain types of hydrocarbons from contaminated sludge. For example, some chemical treatments only allow dissolution of motor oils. Still other chemical treatments only allow dissolution of vegetable oils and animal oils. Accordingly, it is another object of the present invention to develop an alternative method to remove and recover hydrocarbons from a contaminated sludge which allows recovery of numerous different types of oils and hydrocarbons, such as crude oils, motor oils, synthetic oils, graphite oils, vegetable oils and animal oils, from the contaminated sludge, as well as allows the treatment fluid to be reused and recycled. In a preferred aspect, as discussed below, a specific version of the invention yields surprisingly effective results in removing various hydrocarbons from the solid particulates and the aqueous environment.